Atomic Phosphorus Research Articles

Direct determination of phosphorus in biological samples using a solid sampling-high resolution-continuum source electrothermal spectrometer: comparison of atomic and molecular absorption spectrometry

Phosphorus is an element that is difficult to determine accurately by most analytical techniques. In particular, phosphorus determination by means of electrothermal atomic absorption spectrometry (ETAAS) has been traditionally hampered by (i) the practical inability of using phosphorus resonance lines; (ii) its complex chemical behaviour (e.g., formation of volatile compounds and a tendency to interact with graphite); and, particularly, (iii) the overlap observed between molecular and atomic phosphorus lines, which makes it very difficult to obtain reliable results when using line source-ETAAS. In this work, the potential of high resolution-continuum source ET spectrometry for the direct determination of phosphorus in biological solid samples is demonstrated. Two different methodologies, based on the monitoring of either atomic or molecular lines, were compared, paying special attention to the judicious selection of the chemical modifier and the temperature program that will be most adequate to the intended purpose. In order to enable atomic phosphorus monitoring, a high atomization temperature (2650 °C) and a combination of chemical modifiers consisting of palladium, ascorbic acid and tungsten (as permanent modifier) were used. On the other hand, when monitoring PO lines, tungsten coating and vaporization at only 1900 °C proved to be sufficient for attaining reliable results, although attention has to be paid to the possible effect of spectral interferences (e.g., NO lines). Both methods permitted the direct analysis of the samples under investigation, offering a high sample throughput (about 15–20 minutes per determination), good sensitivity (m0 around 5 ng and LODs at the µg g−1 level), RSD values in the 5–10% range, and straightforward calibration with aqueous standards.

レーザアブレーション／レーザ誘起蛍光法の鉄鋼分析への応用―鋼中微量Ｐの検出―

Quantitative detection of phosphorus in steel by Laser ablation–laser induced fluorescence spectrometry has been studied. Solid steel samples were irradiated by pulsed Nd:YAG laser (ablation laser) to generate atomic vapor, which was then illuminated by the probe laser. Laser induced fluorescence spectrum of phosphorus with the highest selectivity was obtained with excitation at 255.49 nm among transitions of atomic phosphorus in 253–256 nm. Dependences of fluorescence intensity on pulse energies of ablation laser and probe laser were investigated. Fluorescence intensity was found to be logarithmically proportional to the ablation laser pulse energy with the slope of 3.2–3.3. Fluorescence intensities were in a good linear correlation with contents of phosphorus in steel samples in a range of 37–350 μg/g. Relative standard deviation were 5.6 and 12.8% at 72 and 170 μg/g of phosphorus, respectively.

Synthesis and Functionalization of Fullerenes Encapsulating Atomic Phosphorus

AbstractSynthesis, purification, and electron spin properties of the endohedral fullerene P@C60 are reported. Highly enriched material could be obtained for the first time, making this molecule accessible for further experiments. We report the first successful chemical modification of P@C60 via cyclo‐propanation to the C2v symmetric monoadducts P@C61(COOCH3) and P@C61(COOC2H5). X‐band electron spin resonance data are presented and discussed. The phosphorus atom shows anisotropic hyperfine coupling in the modified fullerenes, in contrast to the unmodified case, and in contrast to similarly modified N@C60.

Investigation of chemical modifiers for phosphorus in a graphite furnace using high-resolution continuum source atomic absorption spectrometry

Phosphorus is not one of the elements that are typically determined by atomic absorption spectrometry, but this technique nevertheless offers several advantages that make it attractive, such as the relatively great freedom from interferences. As the main resonance lines for phosphorus are in the vacuum–ultraviolet, inaccessible by conventional atomic absorption spectrometry equipment, L´vov and Khartsyzov proposed to use the non-resonance doublet at 213.5 / 213.6 nm. Later it turned out that with conventional equipment it is necessary to use a chemical modifier in order to get reasonable sensitivity, and lanthanum was the first one suggested for that purpose. In the following years more than 30 modifiers have been proposed for the determination of this element, and there is no consensus about the best one. In this work high-resolution continuum source atomic absorption spectrometry has been used to investigate the determination of phosphorus without a modifier and with the addition of selected modifiers of very different nature, including the originally recommended lanthanum modifier, several palladium-based modifiers and sodium fluoride. As high-resolution continuum source atomic absorption spectrometry is revealing the spectral environment of the analytical line at high resolution, it became obvious that without the addition of a modifier essentially no atomic phosphorus is formed, even at 2700 °C. The absorption measured with line source atomic absorption spectrometry in this case is due to the PO molecule, the spectrum of which is overlapping with the atomic line. Palladium, with or without the addition of calcium or ascorbic acid, was found to be the only modifier to produce almost exclusively atomic phosphorus. Lanthanum and particularly sodium fluoride produced a mixture of P and PO, depending on the atomization temperature. This fact can explain at least some of the discrepancies found in the literature and some of the phenomena observed in the determination of phosphorus using line source atomic absorption spectrometry.

The biotin-capture lipid affinity assay: a rapid method for determining lipid binding parameters for apolipoproteins

The lipid affinity of plasma apolipoproteins is an important modulator of lipoprotein metabolism. Mutagenesis techniques have been widely used to modulate apolipoprotein lipid affinity for studying biological function, but the approach requires rapid and reliable lipid affinity assays to compare the mutants. Here, we describe a novel method that measures apolipoprotein binding to a standardized preparation of small unilamellar vesicles (SUVs) containing trace biotinylated and fluorescent phospholipids. After a 30 min incubation at various apolipoprotein concentrations, vesicle-bound protein is rapidly separated from free protein on columns of immobilized streptavidin in a 96-well microplate format. Vesicle-bound protein and lipid are eluted and measured in a fluorescence microplate reader for calculation of a dissociation constant and the maximum number of potential binding sites on the SUVs. Using human apolipoprotein A-I (apoA-I), apoA-IV, and mutants of each, we show that the assay generates binding constants that are comparable to other methods and is reproducible across time and apolipoprotein preparations. The assay is easy to perform and can measure triplicate binding parameters for up to 10 separate apolipoproteins in 3.5 h, consuming only 120 microg of apolipoprotein in total. The benefits and potential drawbacks of the assay are discussed.

Supported (NiMo,CoMo)-carbide, -nitride phases: Effect of atomic ratios and phosphorus concentration on the HDS of thiophene and dibenzothiophene

A study on the catalytic properties of the transition metals (Ni,Co,Mo)-carbides, -nitrides for thiophene and dibenzothiophene hydrotreating was conducted. The (Ni,Co)-Mo carbides and the corresponding (Ni,Co)-Mo nitride phases showed a catalytic activity higher than conventional bimetallic (Ni,Co)-Mo sulfides. In addition, a study was done on the effect of the atomic ratios, i.e., 0.1 ≤ M +/(M + + Mo) ≤ 0.9 where M + stands for Ni or Co, and the concentration of promoters such as phosphorous, which was a structural stabilizing agent. The catalytic performance of the bimetallic NiMo and CoMo carbides and nitrides was studied using thiophene and dibenzothiophene hydrodesulfurization (HDS) as model reactions at 623 K and P = 1 atm. The catalytic activity of the dispersed carbide and nitride phases on the alumina carrier was more significant than that of the reference catalysts, alumina supported NiMo-S and CoMo-S. The metallic character of the NiMo and CoMo carbides was evidenced by their higher hydrogenation activity in thiophene HDS, while the nitrides favored both hydrogenation and hydrogenolysis type reactions.

The influence of defects and postdeposition treatments on the free carrier density in lightly phosphorus-doped large-grained polycrystalline silicon films

The influence of postdeposition treatments (rapid thermal annealing and hydrogenation) on the doping of large-grained polycrystalline silicon p+nn+ thin-film diodes on glass substrates is investigated using resistivity and impedance analysis measurements. Whereas in the lightly phosphorus-doped base region both treatments are found to cause an increase in the active doping concentration, hydrogenation decreases the active doping concentration of both heavily doped layers (Al and P). The different behavior is attributed to acceptorlike defects which are present in the nonhydrogenated base region in a similar concentration as the atomic phosphorus concentration and which are well passivated by hydrogenation. From posthydrogenation annealing experiments and temperature-dependent impedance analysis measurements, different temperature dependences and activation energies (depending on the posthydrogenation annealing temperature) are found for the lightly doped base region. The temperature dependences are quanti...

Dimethyl Methylphosphonate Decomposition on Cu Surfaces: Supported Cu Nanoclusters and Films on TiO2(110)

The thermal decomposition of dimethyl methylphosphonate (DMMP), which is a simulant molecule for organophosphorus nerve agents, has been investigated on Cu clusters as well as on Cu films deposited on a TiO(2)(110) surface. Scanning tunneling microscopy studies were conducted to characterize the cluster sizes and surface morphologies of the deposited Cu clusters and films. Temperature-programmed desorption experiments demonstrated that the surface chemistry of DMMP is not sensitive to the size of the Cu clusters over the range studied in this work. DMMP reaction on an annealed 40 monolayer Cu film resulted in the desorption of H(2), methane, methyl, formaldehyde, methanol, and molecular DMMP, and reaction on the small (4.4 +/- 0.9 nm diameter, 1.8 +/- 0.6 nm height) and large (10.7 +/- 1.9 nm diameter, 4.8 +/- 1.0 nm height) Cu clusters generated similar products. Formaldehyde and methane production is believed to occur via a methoxy intermediate on the Cu surface. These products are favored on the higher coverage Cu films that completely cover the TiO(2) surface since competing reaction pathways on TiO(2) are suppressed. X-ray photoelectron spectroscopy studies showed that DMMP begins to decompose on the Cu clusters upon adsorption at room temperature and that atomic carbon, atomic phosphorus, and PO(x) remain on the surface after DMMP decomposition.

Photoionization of atomic phosphorus from ground and excited states

Resonance structures in the photoionization of atomic phosphorus for the ejection of 3p or 3s electron from the ground 3s23p34So and excited metastable 2Do and 2Po states have been studied in the R-matrix approach. Photoionization cross sections and photoelectron angular distribution asymmetry parameters are dominated by Rydberg series of autoionization resonances converging to several ionic thresholds. There are window resonances due to the 3s3p3(5So)np, 3s3p3(3Do)np and 3s3p3(3Po)np Rydberg series in the inner-shell photoionization from the ground state. Autoionizing states are identified and analysed to obtain resonance positions Er, effective quantum numbers n* and widths Γr using a procedure of eigenphase gradients. Our results for the 3s3p3(5So)np window resonances are in excellent agreement with the experimental values. Total and partial cross sections together with asymmetry parameter for leaving the ion in the ground 3s23p23P state have been calculated in both length and velocity formulations that exhibit very good agreement with each other.

Structure and properties of thin iron phosphide films on carburised layers

Iron phosphate layers on the carbuised layer structure and properties on the carburised layer have been studied. The layers were generated as a result of a gas phosphorcarburising of Armco iron and 0.2% C steel. Calculations have been done on the Gibbs energy of phosphates Fe3P, Fe2P and FeP synthesis reactions. In terms of the value of the Gibbs energy, Fe3P creation as a result of the synthesis of iron and atomic phosphorus P1 is privileged. Fe3P phosphides and a solid solution of phosphorus layer in iron on the carburised layers generation possibility have been suggested. Thin iron phosphide layers increase hardness and decrease friction wear of carburised layers on iron and steels.

Structure and properties of thin iron phosphide films on carburised layers

Iron phosphate layers on the carbuised layer structure and properties on the carburised layer have been studied. The layers were generated as a result of a gas phosphorcarburising of Armco iron and 0.2% C steel. Calculations have been done on the Gibbs energy of phosphates Fe 3P, Fe 2P and FeP synthesis reactions. In terms of the value of the Gibbs energy, Fe 3P creation as a result of the synthesis of iron and atomic phosphorus P 1 is privileged. Fe 3P phosphides and a solid solution of phosphorus layer in iron on the carburised layers generation possibility have been suggested. Thin iron phosphide layers increase hardness and decrease friction wear of carburised layers on iron and steels.

Bonding of atomic phosphorus to polycyclic hydrocarbons and curved graphitic surfaces.

We present a theoretical study of the bonding of atomic phosphorus to planar hydrocarbons and to curved graphite-like surfaces. We find that bonding of phosphorus to planar polycyclic hydrocarbons induces curvature away from the phosphorus atom, as defined by the pyramidalization angle. Similarly, bonding of atomic phosphorus to the [5,5] fulvalene-circulene semifullerene and buckminsterfullerene is only possible on the convex side of the carbon surface. On the other hand, we find the interaction of atomic phosphorus with the concave side of fullerene-like surfaces to be nonbonding for both quartet and doublet spin states. We find the prerequisite for stable epoxy-type bonds within these systems is the ability of the carbon atoms to maintain or induce curvature away from the P.C=C bond.

Effects of mechanical stress on polycrystalline-silicon resistors

Results are presented of a study on the mechanical stress dependence of the resistance of polycrystalline silicon (Poly-Si) films doped with different atomic species, namely, with boron and phosphorus ions. B-doped films of 400 nm and P-doped films of 250 nm thickness were deposited by low-pressure chemical vapor deposition at 620 °C on thermally oxidized silicon wafers. A controlled amount of external stress was applied to the silicon wafers in order to investigate the impact on the electrical performance of the implanted Poly-Si resistors. The resistance of the B-doped Poly-Si films is shown to increase by the mechanical stress, while the resistance of the P-implanted Poly-Si films remained unchanged. It is concluded that this difference is related to the structural differences between Poly-Si films implanted with boron and phosphorus, respectively.

Negative balance of calcium during lactation in marginally nourished women.

Thirty-three rural Mexican women (age, 18-36y; weight, 50.3+/-3 kg; height, 148.3+/-2 cm) were studied under metabolic balance conditions. The objectives were to study the metabolic balances of calcium and phosphorus at the 1st, 3rd, and 6th months of lactation and postweaning and to determine the incorporation of calcium and phosphorus in milk. Subjects were divided into 5 groups of 5 to 10 each, representing: the 1st, 3rd, and 6th month of lactation, postweaning, and a control group of nonpregnant, nonlactating women. Metabolic balance was determined using identical diets and analysis of 24-hour urine (3 d), 72-hour feces, and 24-hour milk samples. Calcium content was determined by atomic absorption spectrophotometry and phosphorus by a colorimetric method. Calcium content in milk was similar at the 1st, 3rd, and 6th months. Positive calcium balances were observed in the control group, while balances were very negative in all lactation groups (-721.6+/-248 mg/d). Calcium urinary excretion was higher in the control and postweaning groups (P < 0.05), suggesting a regulatory mechanism to conserve calcium during lactation. No differences were observed in phosphorus content in milk at the 1st, 3rd, and 6th months. Positive balances were observed in the control and postweaning groups (331+/-139 and 87.1+/-130 mg/d, respectively, mean +/- SD), while the lactation groups presented more subjects (approximately 75%) in negative balance (mean +/- SD of -180.6+/-392 to -439+/-146 mg/d). High fecal calcium and phosphorus excretion (approximately 1,500 mg/d) likely contributed to the negative balance during lactation.

Doping of ZnSe during molecular beam epitaxial growth using an atomic phosphorus source

Zinc selenide films were doped with phosphorus during molecular beam epitaxial (MBE) growth by employing a novel, valved, three-zone solid-source radio frequency (rf)-cracker unit manufactured by Oxford Applied Research (OAR). Optical emission spectroscopy analysis of the plasmas produced in the rf chamber of the unit showed that the apparatus was capable of generating a flux of atomic phosphorus. By suitably adjusting the operating conditions of the unit, phosphorus concentrations in ZnSe epilayers were varied over the range of 1×1016 cm−3 to high-1018 cm−3, in a highly controlled and reproducible fashion. Phosphorus atoms, in contrast to P4 molecules, were found to be highly chemically reactive at the growing ZnSe surface at a normal growth temperature (around 300 °C), and the OAR unit was found to be eminently suitable for the provision of atomic P for MBE growth. Doping using atomic P was found, at least in lightly to moderately doped ZnSe, to provide an acceptor state that gave rise to a neutral-acceptor bound exciton emission located at 2.7919 eV, in keeping with that of other substitutional acceptors in ZnSe. Also, compensation in atomic P doped ZnSe appears to occur by virtue of the formation of shallow donor states rather than via the production of deep level states, which dominate in the case of most of the previously reported phosphorus-doped ZnSe studies.

Electron paramagnetic resonance study of atomic phosphorus encapsulated in [60]fullerene

Well resolved EPR spectra of P@C60 in solution have been recorded, proving that the encased phosphorus atoms are in their quartet spin ground state. The isotropic hyperfine interaction is increased by a factor of 2.5 compared with the values measured for free atoms. An analysis of spin relaxation data reveals that fluctuating zero field splitting (ZFS) interaction induced by collision-induced deformations of the carbon shell constitutes the dominant relaxation mechanism. The variance of the time fluctuating ZFS interaction is about a factor of 10 larger than that observed for N@C60 under identical conditions. Values for the correlation time of the deformation of the fullerene cage range from 5ps to 32 ps in the temperature interval 190-300 K in toluene.

Electron paramagnetic resonance study of atomic phosphorus encapsulated in [60]fullerene

Well resolved EPR spectra of P@C60 in solution have been recorded, proving that the encased phosphorus atoms are in their quartet spin ground state. The isotropic hyperfine interaction is increased by a factor of 2.5 compared with the values measured for free atoms. An analysis of spin relaxation data reveals that fluctuating zero field splitting (ZFS) interaction induced by collision-induced deformations of the carbon shell constitutes the dominant relaxation mechanism. The variance of the time fluctuating ZFS interaction is about a factor of 10 larger than that observed for N@C60 under identical conditions. Values for the correlation time of the deformation of the fullerene cage range from 5ps to 32 ps in the temperature interval 190-300 K in toluene.

Passivation of Fe(110) via phosphorus deposition: the reactions of trimethylphosphite

The reactions of trimethylphosphite, P(OCH 3) 3, with the clean and phosphorus pre-covered Fe(110) surface have been investigated by X-ray photoelectron spectroscopy (XPS), temperature-programmed reaction spectroscopy (TPRS) and low-energy electron diffraction (LEED). P(OCH 3) 3 adsorbs molecularly on the clean surface and remains intact up to a temperature of 250 K at which point it begins to decompose to surface methoxy and atomic phosphorus. Subsequent reaction of methoxy yields gaseous CO and H 2 at 430 K, as well as adsorbed P, C, and O. CO is formed upon heating to ∼770 K from the recombination of atomically adsorbed C and O. The presence of phosphorus on the surface alters the decomposition pathway for molecular trimethylphosphite via a combination of electronic and geometric effects, leading to production of formaldehyde in addition to CO and H 2. The fraction of formaldehyde increases with higher phosphorus coverages. The dependence of the reactions on phosphorus coverage indicated that proximity to adsorbed phosphorus favors formaldehyde production while CO is formed on clean Fe sites. The effect of phosphorus on the reactions of trimethyl phosphite on Fe(110) is similar to the effect of sulfur and oxygen on the reactions of methanol on Fe(100), but different than the effects of sulfur and oxygen on the reactions of methanol on Fe(110), suggesting that adsorbed phosphorus may change the geometric structure of Fe(110). The deposition of phosphorus via irreversible decomposition of P(OCH 3) 3 is self limiting. A maximum of ∼0.35 ML of phosphorus is deposited on the surface at which point the trimethyl phosphite primarily reversibly adsorbs below 500 K. These results indicate that P-containing moieties in lubricant additives form a passivating surface layer upon which the remaining additives only weakly bind.

Casein micelle size in relation with casein composition and αs1, αs2, β and Κ casein contents in goat milk

The relationship between micelle size and casein micelle composition was studied on 21 individual goat milks from animais homozygous for as1casein variants A, B2, C, E, F and O. A large variation in milk composition was obtained, as asl secretion levels varied from 7.2 g-kg! in A milks to none in 0 milks. Mean micelle size (MMS), determined by photon correlation spectroscopy, var- ied between samples from 192 nm to 287 nm. This was explained by the different aspects of the histograms of casein distribution according to the size, determined from transmission electron microscopy data, which showed a maximum either in the low diameter range (20-130 nm) or in the large diameter region (130-260 nm), or even intermediary figures with a bimodal distribution. The caseins, as1CN, as2CN, ~CN and KCN were determined in milks from nitrogen malter determinations (N x 6.38) and RP-HPLC analysis of casein. Polynomial relations were calculated between micelle size and milk composition al parameters. MMS was correlated on one side to the as1CN and KCN lev- els in milks (g-kg') and, on the other side, to the proportions of as1CN %, as2CN % and ~CN % in total casein. These polynomial relations allowed the prediction of the mean micelle size in milks from the casein levels, with aiS % accuracy. Monofactorial correlations also showed a significant effect of as1CN (r = -0.77), but not any of KCN. Mineral composition of milks was determined, calcium by atomic absorption spectrophotometry and phosphorus, by a colorimetrie method. Goat milks were characterized by a constant colloidal inorganic P level (12.4 (SO = 1.7) mmol-kg ). In contrast, colloidal Ca (Cac), SerineP and total colloidal P (Pc) were correlated to the total casein content. The ratio CaclPc was the most constant parameter in goat milks, amounting 1.22 (SO = 0.05), presumably characterizing an unique mode of association of caseins in milk. No significant correlation was obtained between the colloidal Ca and P levels in milks and the size of micelles. © InralElsevier, Paris. / 1 1

Determination of potassium, magnesium, phosphorus, manganese and cation exchange capacity for fertilizer recommendations used by Czech union of rapeseed growers

Abstract The Union of Rapeseed Growers began to use a method of soil testing (KVK‐UF), with a subsequent system of fertilizing, because this approach helped to re‐establish a good level and balance of soil nutrients. The soil nutrients were extracted using neutral 0.5M ammonium acetate containing 0.015M NH4F. Exchangeable cations were determined by atomic absorption and phosphorus as a phosphomolybdate complex. Excess NH4OAc was washed from the soil with ethanol, then the determined exchangeable ammonium ions were related to the CEC of the soil. The relationship between the amount of extractable P and availability for the plant was evaluated in short‐term experiments in plant growth chambers. The best correlation was found in tests using Fe(OH)3‐impregnated paper, followed by the methods: KVK‐UF, 0.01M CaCl2, EUF, Mehlich 2 and Egner (in descending order). The correction determined phosphorus values in KVK‐UF extractant by CEC. of soils improved the degree of correlation. This method, therefore, was the m...